1. Field of the Invention
This invention relates to a process for producing, by a blow molding method, a molded article which can be attached to an outside panel of the body of a vehicle for the purpose of cushioning, prevention of damage or decoration of the vehicle body.
2. Description of the Prior Art
Moldings (molded articles) made of moldable plastics can be obtained by various processes, including extrusion molding, injection molding, blow molding and the like. In recent years, the demand has increased for molded articles which have a beautiful appearance and which match the color of a vehicle body and for molded articles to which characters, a decorative design or the like, have been applied for improving the appearance of the molded articles.
In order to color a molded article, generally, painting is performed separately after molding in most applications of the aforementioned molding methods.
In the case of blow molding, a stripe or projecting ridge is likely to be formed on the molding, caused by an irregular flow of the resin during extrusion of the preform or parison, or by damage to the mold or the like. Also, the transfer pressure to the molding face of a metal mold section is relatively low compared to the pressure during extrusion molding. Consequently, the ridge formed during extrusion molding remains on the surface of the molded article, and accordingly, it is difficult to obtain a flat and smooth surface of the molded article.
In order to remove the air that is present between the parison and the molding face of a metal mold section, an air-bleeding hole is sometimes formed on the molding face of the metal mold section. However, there is a disadvantage that, during blow molding, the adjacent portion of the parison will flow into such an air-bleeding hole and a small projection will be formed on the outer face of the molded product.
Accordingly, surface finish processing is required for such a molded article, as described above, in order to remove the stripe or small projection. When it is desired to color the molded article, also a painting step is required. Therefore, in order to obtain a desired appearance, surface finish processing and painting steps are essential. This is disadvantageous because the number of man-hours required for production of the molded article is increased, the cost of the product is increased, and so forth.
Thus, for the purpose of improving the appearance of the molded article, a method of molding a resin film integrally with the parison, instead of painting, has been invented. However, if a molded article is produced by such a method as described above, the air present between the molding face of a metal mold section and the resin film and the air present between such resin film and the parison cannot be removed and another problem occurs, namely, that the appearance of the molded article is deteriorated. Such phenomenon is likely to take place even when the outer surface of the molded article is very rough in shape. There is a tendency that such a phenomenon will take place, particularly around a convex portion of the molded article.
It has also been found out that, as the height dimension of the molded article increases, that is, as the dimension from the mounting face to the top portion of an outer surface becomes larger, the formation of a satisfactory coating of a resin film becomes more difficult, and whitening or breaking, by elongation of the resin film, takes place.
Accordingly, it is an object of the present invention to provide a process of producing a molded article having a good appearance by using a resin film in a blow molding method.
It is another object of the present invention to provide a process which can remove the air which remains when a resin film is placed on the parison.
It is a further object of the present invention to provide a process of preventing whitening and breaking of the resin film.